Electrostatic stylus recording with self-cleaning drum

ABSTRACT

A method of electrostatic recording using signal energised styli adjacently disposed across the surface of a photoconductive recording member so that such surface receives a recording potential to form a latent electrostatic image thereon, then rendering the latent image visible by applying electroscopic marking particles, then transferring the image so formed onto another surface, and cleaning the recording member for further recording by removing residual marking particles and by removing residual electrostatic charges by lowering the electrical resistivity of the photoconductive layer by exposure to activating radiation during a corona discharge.

United States Patent 1 Matkan et al.

[4 1 Feb. 12,1974

ELECTROSTATIC STYLUS RECORDING WITH SELF-CLEANING DRUM Inventors: JosefMatkan, Malvern; Kevin Douglas OConnor, Queenstown, both of AustraliaCanon Kabusliiki Kaisha, Tokyo, Japan Filed: Apr. 22, 1971 Appl. No.:136,325

Assignee:

Foreign Application Priority Data May 1, 1970 Australia 1075/70 U.S. Cl.346/74 ES, 355/15 Int. Cl G03g 13/22 Field of Search... 346/74 ES, 8 P;250/4952 C;

References Cited UNITED STATES PATENTS ll/l967 Hall et al 346/74 P [57]ABSTRACT A method of electrostatic recording using signal energisedstyli adjacently disposed across the surface of a photoconductiverecording member so that such surface receives atrecording potential toform a latent electrostatic image thereon, then rendering the latentimage visible by applying electroscopic marking particles, thentransferring the image so formed onto another surface, and cleaning therecording member for further recording by removing residualmarkingparticles and by removing residual electrostatic charges bylowering the electrical resistivity of the photoconduc-,

tive layer by exposure to activating radiation during a coronadischarge.

8 Claims, 3 Drawing Figures Clark 346/74 ES PAIENIEDFEBI 2 7 3.792.494

' sum 2 [1F 2 1 LECTROSTATIC T L R C R WITH SELECLEANING DRUM Thisinvention relates to signal recording and in particular relates to amethod whereby the final visual record of such signals may be obtainedon any desired surface.

Signal recording methods are known in which transmitted information inbit or character form is fed into a receiving station and recorded on areceiving member v in the form of a latent electrostatic image, suchimage impression being produced by the'application of electrical energypulses to selected styli, which styli may be in contact with therecording member in those instances where relatively low voltage pulsesare used, or alternatively may be placed apart from the recording memberin which instances it is usual to use relatively high voltage pulses.

The recording member used in conjunction with such prior art meansconsists of a paper or other conductive backing member having one sidethereof a thin continuous layer of insulating material, such assynthetic resin orthe like, which insulating layer is capable ofsupporting the impressed pattern of electrostatic charge correspondingto the transmitted information for at least suffieient'time to allowdevelopment of such latent image. The latent image is subsequentlyrendered visible by development with a dry or liquid dispersed tonermaterial such as those well known in the art of electrophoqg aphy- Y Afurther form of signal recording apparatus utilises anelectrophotographicrecording member such as a Selenium plate or resinbound particulate photoconductor, in which instance the transmittedinformation is converted to light and selectively transmitted to theelectrophotographic recording member by the use of a cathode ray tubeflying spot scanner ora fibre optics array or the like, thephotoconductor surface having been given a uniform electrostatic chargeon its sensitive surface prior to this selective exposure. The thusproduced latent imageis developed with a dry or liquid dispersed tonermaterial as previously described. In some instances the thus developedimage is transferred to a sheet of plain paper or the like, and thus thephotoconductor surface is rendered available for further imaging.

The prior art processes exhibit certain disadvantages which it is theprime object of this invention to overcome. In the first mentioned priorart process the image is produced on a specially treated paper, whichpaper is relatively expensive in comparison with plain paper. It wouldbe advantageous in such equipments to use a permanent recording memberand transfer the developed image to a sheet of plain paper, however, itis dif ficult to erase images produced on insulator surfaces to asufficient extent to allow subsequent re-imaging without alsoredeveloping the previous image. The second mentioned prior art processcan produce copies on plain paper, but the electrophotographic imagingmethods are relatively slow in operation and require high intensitylight sources severely confined in area to produce images of reasonabledefinition. In addition cathode ray tubes and fibre optic arrays areeach relatively expensive and fragile.

We have now found that electrostatic imaging techniques such as those ofthe first mentioned prior art processes can be used in conjunction withcertain photoconductor recording members in a manner not previouslyknown whereby the high speed and high definition latent image formingcapabilities of such stylus impression methods may be used to image aphotoconductive recording member, following which the latent image maybe developed as previously described and transferred to a sheet of plainpaper or the like. The photoconductor properties of the recording membermay then be used to remove residual electrostatic patterns on thesurface thereof prior to the receipt of further information to berecorded.

The recording member in accordance with one embodiment of this instantinvention comprises a conductive or relatively conductive basecontaining on one side thereof a photoconductive layer or coating andsaid photoconductive layer containing on its surface remote from saidconductive base a further layer or coating of a relatively thininsulating material. Such recording member is capable of acceptingimagewise electrostatic charges corresponding to signals impressed fromstyli in presence or in absence of light in view of the aforesaidinsulating layer contained over said photoconductive layer.

The recording member may have rectifying properties and in case thephotoconductor is of the n-type the applied signals can be of positivepolarity whereas in case the photoconductor is of the p-type the appliedsignals can be of negative polarity. In each case imagewisecorresponding electrostatic charges having a polarity opposite to thepolarity of the charges contained on the surface of the insulating layerwill be induced at the interface between the insulating layer and thephotoconductive layer.

The image-wise charges contained on the surface of the insulating layercan be developed or rendered visible by the application thereto ofelectroscopic marking particles which can be of the dry or liquid typeas commonly known in the art of electrophotography and in common use inoffice copying machines and the like.

The developed image can be transferred to plain paper or other imagereceiving copy material and such transfer operation can be carried outin the presence of an assisting electrostatic field.

Depending on the developing and transfer methods used it is possible toobtain more than one transfer copy from the one impressed charge patternif so desired.

Such multiple copies can be obtained in one instance by the successivetransfer of partially developed images wherein such partial developmentallows for redevelopment of residual charges to be carried out and insuch instances it is necessary to adjust the transfer conditions and inparticular the transfer assisting potential to prevent distortion ordestruction of the residual charge.

In other instances multiple copies can be obtained by the successivetransfer of parts only of the developed image and in this case it isalso necessary to adjust the transfer conditions and in particular thetransfer assisting potential to regulate the quantity of tonertransferred in order to obtain more than one transfer copy.

Employing either method of transfer it has been found possible to obtainin excess of six legible copies from one imaging step.

Prior to the impression of further signals the residual charges of thepreceding image can be erased by subjecting the recording member to acorona discharge or the like and simultaneously illuminating saidrecording member surface in order to render the photoconductive layerconductive. The polarity of the corona discharge potential should beopposite to that employed for imaging or at least contain a component ofsuch opposite polarity. Alternating current corona discharge can be usedif desired.

The recording member in accordance with another embodiment of thisinvention comprises a conductive or relatively conductive basecontaining on one side thereof a layer of a photoinsulator upon whichthe image-wise charges can be impressed as in the first embodiment butin the absence of light. It will be realised that a photoinsulator is aphotoconductor with sufficiently high dark resistivity to hold anelectric charge on its surface in the dark. The charge images can bedeveloped and transferred, if desired, as described in connection withthe first embodiment above, provided such steps for multiple transferare carried out in the absence of light. The residual charges may beremoved by overall exposure to light.

The photoconductive layer may consist of a selenium, cadmium sulfide,cadmium selenide, zinc oxide and the like, and may be in powder formincorporated with a film forming resinous binder. Alternatively certainphotoconductors may be formed into continuous films by vacuumevaporation, sintering, sublimation and the like. In addition organicphotoconductors may be used if desired. The speed of response of thephotoconductors may be enhanced by the inclusion of sensitizing agentsas is well known in prior art relating to photoconductive films orlayers, the sensitising agents being for instance such materials ascertain organic dyes or impurity additions within the crystal lattice,such as the metal radicles included as impurities for the purpose ofsensitising, or doping as it is commonly referred to, as is well knownin relation to cadmium sulfide photoconductive layers.

The insulating layer of the first embodiment which is maintained inintimate contact with the photoconductive layer, is a material ofsufficiently high resistivity to support electrostatic charges on itssurface and in addition is at least translucent to the light used toerase the residual charge images. Suitable materials are polyesterresins, fluorocarbon resins, cellulose acetate, vinyl resins and thelike, with surface resistivities generally in excess of lO ohm/sq.centimeter. The thickness of such insulating film is such that it formsa continuous film over the photoconductive layer and no breakdown occurswhen the signal charges are applied, and is typically within the range50 microns, it having been found that films of a thickness of less than10 microns often contain discontinuities such as pinholes and the like,whereas films greater than 50 microns in thickness may not be completelydischarged by the combined action of light and corona due to capacitanceeffects.

In order that the invention may be more readily understood referencewill now be made to the drawings.

FIG. 1 illustrates the first embodiment of this invention in the form ofa continuous machine, and it will be realised that certain features areillustrated'by way of example only, and should not be read in thelimiting sense;

FIG. 2 is a plan of the multiple stylus assembly and switch means;

and FIG. 3 is a view similar to FIG. 1 but showing a modified form.

Referring to FIG. 1 and 2 in detail, a conductive drum 1, is rotatablymounted on an axle, 2, to rotate in a clockwise direction as shown. Aphotoconductive layer, 3, is contained on the outer surface of the drum1, and is in turn overlain with a continuous insulating layer 4. Alinear array of writing styli 5, see particularly FIG. 2, are positionedto be in nominal contact with the cylindrical outersurface of insulatinglayer 4, and each stylus is independently connected to a DC power supply7, through independent switching means 6, such switching means beingcontrolled by an input signal, the other terminal of the DC power supply7, being connected to the conducting drum 1, and grounded. When the drum1 is rotated in a clockwise direction the insulating layer 4 is moved inrelation tothe various components of the system, and thus each sectionof the said insulator 4 passes the writing styli 5, at which position anelectrostatic latent image corresponding to the input signal is producedon the surface of the insulator 4. The electrostatic latent image isdeveloped on the insulating surface by the attraction of electroscopicpowder thereto, which may be brought about by contacting said insulatorsurface with a roller 9, which roller is partially immersed in a bath10, containing a suspension of electroscopic marking particles in aninsulating carrier liquid 11, such as is well known in the art ofelectrophotography, and is in common use in electrophotographic officecopying machines and the like.

After development the image bearing insulating surface contacts apaperweb 12, which may be in the form ofa continuous web, or in sheets asdesired, contact between the paper web 12, and the developed surface ofinsulator 4, being maintained by roller 13.

In addition roller 13, is connected to a transfer DC power supply 14,whereby an electrostatic field may be applied at the transfer nip tocause the transfer of the developed image from the insulator surface 4,to the paper web 12. The plain paper copy of the information isdelivered to outlet tray 15.

Further rotation of the drum 1 causes the areas of the insulator surface4 from which the image has been transferred to contact a cleaning means16, whereby residual toner deposit on the insulator surface may beremoved. Such cleaning means 16 may be in the form of a revolving brush,or a scraper blade, as desired.

Before being reimaged the insulating surface 4 passes an electrostaticcleaning means, consisting of an exposure lamp l7 and a corona wire orseries of corona points 18, positioned to influence the recording membersimultaneously. The corona generating means 18 is connected to a highvoltage power supply 19, and the combined influence of corona generatingmeans 18 and light 17 discharges the residual electrostatic chargesexisting on the insulating surface 4 under the influence of thephotoconductor layer 3. The photoconductive layer 3, under the influenceof light, provides a conductive path whereby the surface chargesexisting on the surface of insulator 4 may be removed by the coronadischarge from the corona generating means 18, when such coronagenerating means generates a field with a component of opposite polarityto that impressed on the insulator 4 by the writing styli 5.

FIG. 3 illustrates the second embodiment of this invention, in which thephotoconductor layer 103 on the conducting drum 101 is of sufficientlyhigh electrical resistivity to retain the electrostatic latent imagewithoutthe use of an overlying insulating film. In this instance thephotoconductor layer 103 will be shielded from light during charging,developing, and transferring of the image. It will be seen that in thisembodiment electrostatic cleaning of the photoconductor surface 103prior to reimaging is carried out by the use of an exposing light only,as the neutralising corona discharge of the first embodiment is notrequired in the absence of the overlying insulator film of the firstembodiment.

FIG. 3 also illustrates an alternative developing system, in which theliquid dispersed toner 111 is contained within tank 120, from which itis pumped using the pump 121, to pass through the inlet pipe 122 to passover the curved plate 123, which plate is in close proximity to thesurface of photoconductor layer 103. Unused toner suspension returns totank 120 through the overflow pipe 124. g

It will be realised that many developing mechanisms are known by whichliquid dispersed or dry electroscopic marking particles may be presentedto a surface to be developed, and many of these mechanisms may be usedin the present invention without departing from the spirit thereof.

The following examples will serve further to illustrate the principlesof the invention.

EXAMPLE 1 This example refers to the first embodiment of this invention.A recording member was prepared by coating a metal drum with a layer ofphotoconductive cadmium sulfide in a polyester resin binder, thethickness of this layer being 100 microns. A micron polyester film wasbonded to the outer surface of said photoconductor layer, to provide acontinuous insulating layer thereon. A linear array of writing styli waspositioned so that the end of each stylus was in nominal contact withthe insulating layer. The styli were 0.007 inch diameter at 0.010 inchcentre spacings, and each stylus was connected to a power supply throughindependent switching means capable of actuation by an input signal. Thevoltage applied to the styli was of positive polarity, adjustable withinthe range 0 500- volts. The drum was rotated and a signal used to selectand activate individual styli to produce an electrostatic latent imageon the insulator surface. The latent image was developed by applicationof a liquid dispersed toner in which the electroscopic marking particleswere of negative polarity in suspension. Such toners are well known.

The developed image deposit was transferred to a plain paper web bycontacting said paper web with the wet developed image under theinfluence of a transfer voltage of 100 volts.

Residual toner deposit was subsequently removed from the insulatingsurface using a rotating brush, and residual electrostatic charges wereremoved from the surface of the recording member prior to reimaging bythe combined action of an AC corona potential of 7kV and light.

The surface was then reimaged, and it was found that the previous imagehad been completely removed. EXAMPLE 2 The method of Example 1 wasrepeated using a negative DC corona of 5kV in combination with light toerase residual electrostatic charges on the recording member surface.EXAMPLES 3 and 4 The photoconductor of Examples 1 and 2 was replacedwith a 50 micron layer of vitreous selenium, and in these instances thepolarity of the writing voltage was reversed, as also was the polarityof the erasing voltage in that instance when DC was used for erasingpurposes. EXAMPLES 5 and 6 The photoconductor of Examples 1 and 2 wasreplaced with a polyvinyl carbazole organic photoconductor. EXAMPLES 7and 8 The photoconductor of Examples 1 and 2 was replaced withphotoconductive zincoxide in an insulating resin binder. EXAMPLE 9 Thisexample refers to the second embodiment of this invention. Thephotoconductor used was vitreous selenium, which was imaged using apositive polarity ap' plied to the selected styli in the absence oflight. The writing voltage used was within the range 5 500 volts. Theprocessing steps were substantially as used in Example l, with theexception that residual electrostatic charges on the recording membersurface were removed before reimaging by the application of light only.

EXAMPLE 10 The photoconductor of Example 9 was replaced with a layer ofphotoconductive zinc oxide in an insulating resin binder, and thewriting voltage was of negative polarity.

EXAMPLE ll A dye sensitised zinc oxide photoconductor layer wassubstituted for the photoconductor of Example 10.

The recordingmember of either embodiment can be in the form of a flatplate or a rotatable cylinder or the like over which the signal chargesare impressed and the developing, transferring and discharging stationscan be arranged conveniently to suit any desired configuration. Ineither embodiment a signal recording system may be used in which astylus may contact the surface of the recording member. Individual stylimay be within the range of 0.075 mm to 0.2 mm, centre spacing 0.25 mm,and the signal voltage. may be within the range 5V to 1,000V, appliedtypically for periods within the range 1 microsecond to 5 milliseconds,the higher voltages being used advantageously in conjunction with thesmaller diameter styli.

We claim:

1. A method of electrostatic recording comprising the steps ofenergizing styli adjacently disposed across the surface of a recordingmember containing a photoconductive layer by input data signals toselectively charge electrostatically with a recording potential saidsurface of said recording member to form a latent electrostatic imagethereon, rendering visible said electrostatic latent image by applyingthereto electroscopic marking particles, transferring such image formedby said marking particles onto another surface, cleaning said surface ofsaid recording member to remove residual marking particles therefrom andremoving residual electrostatic charges from said surface of saidrecording member by lowering the electrical resistivity of saidphotoconductive layer contained in said recording member by exposure toactivating radiation, characterized by a continuous layer of asubstantially transparent insulating material forming said surface ofsaid recording member wherein said insulating layer is contained oversaid photoconductive layer and wherein the electrical resistivity ofsuch insulating material is sufficiently high to permit said surface toretain said electrostatic image formed thereon, further characterised inthat the residual electrostatic charges are removed from said surface ofsaid recording member by the combined action of exposure of saidphotoconductive layer to activating radiation and simultaneousapplication of a corona discharge.

2. A method of electrostatic recording according to claim 1 wherein thepolarity of said corona discharge simultaneously applied with exposureto activating radiation is opposite in sign to that of said latentelectrostatic image.

3. A method of electrostatic recording according to claim 1 wherein saidcorona discharge simultaneously applied with exposure to activatingradiation contains electrical components having a polarity opposite insign to that of said latent electrostatic image.

4. A method of electrostatic recording according to claim 1characterised in that the photoconductor of said photoconductive layeris cadmium sulfide and has over it a continuous layer ofa substantiallytransparent insulating material forming said surface of said recordingmember, the electrical resistivity of such insulating material beingsufficiently high to permit said surface to retain said electrostaticlatent image formed thereon.

5. A method of electrostatic recording according to claim 1characterised in that the photoconductor of said photoconductive layeris cadmium sulfide and has over it a continous layer of polyester resinwhich forms the surface of said recording member, and has an electricalresistivity sufficiently high to permit said surface to retain saidelectrostatic latent image formed thereon.

6. A method of electrostatic recording according to claim 1 in which thephotoconductor of said photoconductive layer is chosen from the group;vitreous selenium, zinc oxide, cadmium selenide or an organicphotoconductor.

7. A method of electrostatic recording according to claim 1 wherein thephotoconductor of said photoconductive layer is sensitized by theaddition of a dye or by doping.

8. A method of electrostatic recording according to claim 1 wherein theinsulator applied over the photoconductor has a resistivity in excess oflO ohmlsquare centimeter and a thickness of 10 to 50 microns and istaken from the group: polyester resins, fluorocarbon resins, celluloseacetate, and vinyl resins.

1. A method of electrostatic recording comprising the steps ofenergizing styli adjacently disposed across the surface of a recordingmember containing a photoconductive layer by input data signals toselectively charge electrostatically with a recording potential saidsurface of said recording member to form a latent electrostatic imagethereon, rendering visible said electrostatic latent image by applyingthereto electroscopic marking particles, transferring such image formedby said marking particles onto another surface, cleaning said surface ofsaid recording member to remove residual marking particles therefrom andremoving residual electrostatic charges from said surface of saidrecording member by lowering the electrical resistivity of saidphotoconductive layer contained in said recording member by exposure toactivating radiation, characterized by a continuous layer of asubstantially transparent insulating material forming said surface ofsaid recording member wherein said insulating layer is contained oversaid photoconductive layer and wherein the electrical resistivity ofsuch insulating material is sufficiently high to permit said surface toretain said electrostatic image formed thereon, further characterised inthat the residual electrostatic charges are removed from said surface ofsaid recording member by the combined action of exposure of saidphotoconductive layer to activating radiation and simultaneousapplication of a corona discharge.
 2. A method of electrostaticrecording according to claim 1 wherein the polarity of said coronadischarge simultaneously applied with exposure to activating radiationis opposite in sign to that of said latent electrostatic image.
 3. Amethod of electrostatic recording according to claim 1 wherein saidcorona discharge simultaneously applied with exposure to activatingradiation contains electrical components having a polarity opposite insign to that of said latent electrostatic image.
 4. A method ofelectrostatic recording according to claim 1 characterised in that thephotoconductor of said photoconductive layer is cadmium sulfide and hasover it a continuous layer of a substantially transparent insulatingmaterial forming said surface of said recording member, the electricalresistivity of such insulating material being sufficiently high topermit said surface to retain said electrostatic latent image formedthereon.
 5. A method of electrostatic recording according to claim 1characterised in that the photoconductor of said photoconductive layeris cadmium sulfide and has over it a continous layer of polyester resinwhich forms the surface of said recording member, and has an electricalresistivity sufficiently high to permit said surface to retain saidelectrostatic latent image formed thereon.
 6. A method of electrostaticrecording according to claim 1 in which the photoconductor of saidphotoconductive layer is chosen from the group; vitreous selenium, zincoxide, cadmium selenide or an organic photoconductor.
 7. A method ofelectrostatic recording according to claim 1 wherein the photoconductorof said photoconductive layer is sensitized by the addition of a dye orby doping.
 8. A method of electrostatic recording according to claim 1wherein the insulator applied over the photoconductor has a resistivityin excess of 1010ohm/square centimeter and a thickness of 10 to 50microns and is taken from the group: polyester resins, fluorocarbonresins, cellulose acetate, and vinyl resins.